The present invention relates to blasting operations wherein a network of detonating cord is strung from a blast initiating position to a plurality of charges that are positioned down in a plurality of separate blast holes. Blast holes, of course, must first be drilled, the explosive loaded into each, a primer and detonating cord placed on top of each charge, and each hole sealed to confine the explosion. The detonating cord can be broken in the hole where it is impossible to observe, particularly when sealing stemming is rammed on top of the primer; and it is also possible for an unobservable defect or break to occur in the section of detonating cord running across the top of the ground. Detonating cord has been used for many years. More recently electrical wires and blasting caps have been used to set off the charges electrically. It is possible to check the continuity of the electric wires by low energy current, but a number of accidents have occurred when lightning or inadvertant stray current has struck the system before ignition. The art has progressed to setting off larger and larger numbers of explosive charges at one time. This has resulted in explosive charges being left undetonated due to faulty wiring, breaks in the detonating cord, etc. When this occurs, the charges must be either rendered harmless, or retrieved or detonated separately before the excavating crew can safely enter the area. The work of deactivating live charges that are left after a blast constitute a considerable hazard to the deactivating crew.
An object of the present invention is the provision of a new and improved detonation system whose continuity can be checked before blast initiation, and which is unlikely to be set off by lightning or stray electrical currents.
Further objects and advantages of the invention will become apparent to those skilled in the art to which the invention relates from the following description of applicants' preferred embodiments described with reference to the accompanying drawings.